Arginine shows no benefit for sickle cell acute pain crises in phase 3 trial

A large multicenter trial testing intravenous arginine as a treatment for acute pain crises in sickle cell patients has ended early, after investigators found no meaningful difference in recovery time between patients who received the amino acid and those who received a placebo, according to results published in JAMA.

Approximately 100,000 people in the United States live with sickle cell disease, according to the Centers for Disease Control and Prevention, and more than 90% of patients are non-Hispanic Black or African American. Life expectancy is more than 20 years shorter, creating a major healthcare disparity.

Episodes can be extremely painful, and as a result, pain crises drive the bulk of hospital-related admissions, often requiring repeat emergency department visits and inpatient stays.

An interest in arginine grew out of smaller trials suggesting the amino acid could treat the vascular blockages caused by the disease, potentially cutting hospital stays and pain scores while reducing the need for opioids. That earlier evidence was strong enough to earn arginine an orphan drug designation from the FDA in 2024, setting up this 3-year-long confirmatory study.

The study, conducted at emergency departments across 10 U.S. children's hospitals, was led by Claudia R. Morris, M.D., from the Emory University School of Medicine in Atlanta. Morris and her team randomized 271 patients, ages 3 to 21, 1:1 to receive either intravenous arginine or intravenous saline, starting with a 200 mg/kg dose and continuing at 100 mg/kg every eight hours until discharge, for up to 21 total doses. Of the 271 enrollees, 129 received arginine and 142 received a placebo. The primary measure of success was the number of hours between a patient's first dose and their last IV opioid dose and, secondarily, total opioid use, pain ratings and patient-reported well-being.

The results showed little separation between groups. It took approximately 60.8 hours for patients given arginine to recover enough to stop needing IV pain medication, versus 65.8 in placebo patients. Opioid requirements were similar, with median doses of 1.4 mg/kg in the arginine group versus 1.0 mg/kg for placebo. There was no gap in pain scores, composite Patient-Reported Outcomes Measurement Information System measures of pain interference, pain behavior, fatigue or adverse events. Outcomes also varied heavily by site, with hospital-level differences reaching 61 hours in medians to 80 hours in means, a variability the authors said would have required enrolling more than 900 patients to reliably detect the 17-hour improvement the trial was designed to find.

"To date, all US-based phase 3 RCTs targeting SCD acute pain have failed to demonstrate an effect on shortening hospital length of stay or time to crisis resolution after promising results from phase 2 trials," Morris and her team wrote in the study. "The current trial is the latest addition to this list, stopped early for futility to achieve its primary endpoint."

Morris and her team pointed to several factors that may have masked a true treatment effect, including wider-than-expected variation and confounding across sites, generally brief hospital stays and inconsistent timing of pain assessments that didn't account for recent analgesic dosing. A high rate of chronic pain in the study population, reported by 41% of participants overall and a third of children under 12, may have further limited the trial's ability to isolate a benefit, since not all sickle cell pain stems from the vaso-occlusive process the drug was designed to target.